1. Field of the Invention
This invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a high-density LSI with microscopic interconnections.
2. Description of the Related Art
In conventional semiconductor devices, for example, DRAM memory cells with bit lines have the structure as shown in FIGS. 1A through 1C. FIG. 1B is a sectional view taken along line 1B--1B of FIG. 1A, and FIG. 1C is a sectional view taken along fine 1C--1C of FIG. 1A. Numeral 701 indicates a p-type semiconductor substrate, 702 an element isolating oxide film, 703 a silicon oxide film, 704 the gate electrode of a MOS FET, 705 an n-type diffused layer, 706A and 706B interlayer insulating films, 707A and 707B contact holes, 708 the bottom electrode of a capacitor, 709 a capacitor insulating film, 710 the top electrode of the capacitor, and 711 a bit line.
On the memory cell, a flattened interlayer insulating film, such as a BPSG film, is generally formed. Formed on the insulating film are metal interconnections (of, for example, aluminum), on which a passivating film is formed to complete the DRAM. Referring to FIGS. 1A through 3B, a manufacturing method of DRAMs will be explained hereinafter, covering all the way to the final products.
As shown in FIG. 1B, the element isolating oxide film 702 is first formed on the p-type semiconductor substrate 701. On an element region of the p-type semi-conductor substrate 701, the silicon oxide film 703, gate electrode 704, and n-type diffused layer 705 are each formed in a known manner to complete the MOS FET. After the interlayer insulating film 706A is formed all over the surface, the contact hole 707A leading to the n-type diffused layer (source) 705 is made. At the contact hole 707A, the bottom electrode 708 of the capacitor, capacitor insulating film 709, and the top electrode 710 of the capacitor are formed to produce a cell capacitor of the DRAM. Over the whole surface, the interlayer insulating film 706B is formed, and then the contact hole 707B reaching the n-type diffused layer (drain) 705 is made. After this, on the interlayer insulating film 706B and contact hole 707B, the bit line 711 is formed by sputtering with silicide such as MoSi.sub.2 or WSi.sub.2.
Then, as shown in FIG. 2A, over the entire surface, the interlayer insulating film 712 such as silicate glass (BPSG film) containing, for example, boron (B) or phosphorus (P) is formed. The interlayer insulating film 712 has larger steps in the vicinity of the bit line 711 as shown in FIG. 2B.
Next, as shown in FIGS. 3A and 3B, high-temperature heat treatment (annealing) is performed in an oxidizing atmosphere to flatten the surface of the interlayer insulating film 712. At this time, an oxidizer (e.g., oxygen) penetrates the interlayer insulating film 712 and oxidizes the bit line 711 made of a silicide film. As a result, on the surface of the bit line 711, the oxide film 713 is formed. The metal interconnections (made of, for example, Al) 714 are formed on the flattened interlayer insulating film 712. Over the entire surface, the passivating film 715 is formed to complete the DRAM.
With the aforementioned manufacturing method, however, it is known that the bit line 711 formed by sputtering has a poor step coverage, with the thickness of the bit line 711 being thinner on the sidewall of the contact hole 707 than on the top surface. In this state, when heat treatment is carried out in an oxidizing atmosphere, the thinner portions of the bit line 711 on the sidewall of the contact hole 707B are all oxidized, leading to breaks in interconnections and an increase in the resistance. Because of this, neither sufficient yield nor high reliability can be achieved.
As noted above, conventional semiconductor devices have a poor step coverage of interconnections at the contact holes. Because of this, a subsequent heat treatment causes the oxidizer to react upon the interconnections to form an oxide film, which results in breaks and increase in the resistance at the thinner portions of the interconnections in the contact holes.